Rest-frame far-ultraviolet to far-infrared view of Lyman break galaxies at z = 3: Templates and dust attenuation

Aims. This work explores, from a statistical point of view, the rest-frame far-ultraviolet (FUV) to far-infrared (FIR) emission of a population of Lyman-break galaxies (LBGs) at z ∼ 3 that cannot be individually detected from current FIR observations. Methods. We performed a stacking analysis over a sample of ∼17 000 LBGs at redshift 2.5 < z < 3.5 in the COSMOS field. The sample is binned as a function of UV luminosity ( L FUV ), UV continuum slope ( β UV ), and stellar mass ( M * ), and then stacked at optical ( B V r i z bands), near-infrared ( Y J H K s bands), IRAC (3.6, 4.5, 5.6, and 8.0 μ m), MIPS (24 μ m), PACS (100 and 160 μ m), SPIRE (250, 350, and 500 μ m), and AzTEC (1.1 mm) observations. We obtained 30 rest-frame FUV-to-FIR spectral energy distributions (SEDs) of LBGs at z ∼ 3, and analyzed these with the CIGALE SED-fitting analysis code. We were able to derive fully consistent physical parameters, that is, M * , β UV , L FUV , L IR , A FUV , star formation rate, and the slope of the dust attenuation law; we built a semiempirical library of 30 rest-frame FUV-to-FIR stacked LBG SEDs as functions of L FUV , β UV , and M * . Results. We used the so-called IR-excess (IRX ≡ L IR / L FUV ) to investigate the dust attenuation as a function of β UV and M * . Our LBGs, averaged as a function of β UV , follow the well-known IRX– β UV calibration of local starburst galaxies. Stacks as a function of M * follow the IRX– M * relationship presented in the literature at high M * (log( M * [ M ⊙ ]) > 10). However, a large dispersion is shown in the IRX– β UV and IRX– M * planes, in which the β UV and M * are combined to average the sample. Additionally, the SED-fitting analysis results provide a diversity of dust attenuation curve along the LBG sample, and their slopes are well correlated with M * . Steeper dust attenuation curves than Calzetti’s are favored in low stellar mass LBGs (log( M * [ M ⊙ ]) < 10.25), while grayer dust attenuation curves are favored in high stellar mass LBGs (log( M * [ M ⊙ ]) > 10.25). We also demonstrate that the slope of the dust attenuation curves is one of the main drivers that shapes the IRX– β UV plane.